1. Field of the Invention
This invention relates generally to soldering irons and soldering stations used in modern electronic production, rework and repair applications which are temperature controlled, but primarily relates to those with closed-loop temperature control for which a defined level of temperature accuracy is desirable, or which are, in certain circumstances, required to be calibrated periodically for the purpose of confirming or re-establishing compliance with various performance standards which include, among other things, proper tip grounding, EMF leakage, temperature stability and a defined level of absolute temperature accuracy between the temperature set or indicated on a control/display device (typically a dial or digital readout) and the actual temperature of the working end of the tip as measured by a more direct, independent means, such as an embedded or spot welded thermocouple, contact pyrometer or some other means.
2. Description of Related Art
For modern, high-reliability electronic production, rework and repair applications, closed-loop temperature controlled soldering irons and stations (hereinafter, xe2x80x9csoldering stationsxe2x80x9d shall also include xe2x80x9csoldering ironsxe2x80x9d) have become the generally accepted norm due to their ability to maintain a safe, appropriate, user-selected tip operating temperature for the particular application at hand. Such traditional soldering stations generally consist of a power supply with a temperature control/display device, typically a dial or digital display which is powered by ordinary line power, and a soldering iron which is connected to the power supply by a power cord and is typically but not always a low voltage supply.
The soldering iron contains a handle and a closed-loop temperature controlled heater to which a replaceable soldering tip is attached through various means, examples of which include the products made by WELLER(copyright), PACE(copyright) and HAKKO(copyright). The traditional closed-loop temperature control means may consist of a thermocouple, resistive temperature detector (RTD) or other sensor embedded into the soldering iron heater, a closed-loop resistive control system such as that found in assignee""s discontinued product known as the Micro Portable soldering/desoldering system, or other means.
Newer products which feature a combined tip/heater cartridge (for which the entire tip/heater cartridge is changed when the tip wears out) may utilize similar temperature control means or alternatively, may feature a Curie point control, such as the tip/heater cartridge product of METCAL INCORPORATED, or a combined heater/thermocouple arrangement such as that found in U.S. Pat. No. 5,043,560 (Masreliez) and in the Model 941 soldering station of the Hakko Corporation; see also, U.S. Pat. No. 4,839,501 of METCAL(copyright) and commonly owned, co-pending U.S. patent application Ser. No. 09/972,194. Compared with traditional soldering stations, tip/heater cartridge stations offer a slim, light weight often cooler handpiece which some operators prefer.
All of these soldering stations, however, suffer from the same or similar problems during use in that their temperature accuracy is less than what may be desired by the user, or that they require periodic calibration to confirm or re-establish compliance with defined performance standards which, among other things, typically include a defined level of temperature accuracy between the desired or selected operating tip temperature, and the true operating temperature (measured at equilibrium or xe2x80x9cidlexe2x80x9d) as measured at the working end of the soldering tip by some other independent means as discussed above. One such standard for absolute temperature accuracy may be found in ANSI-J-STD-001B (and later revisions) in which xe2x80x9cOperator selected or rated temperatures of soldering systems at idle/standby should be within +/xe2x88x9215xc2x0 C. of actual measured tip temperature.xe2x80x9d Of course, users can and often do select different absolute temperature accuracy standards to suit their own particular needs. i.e., the displayed temperature and the actual temperature measured independently at the tip end with an embedded thermocouple must be within +/xe2x88x9215 degrees Centigrade (27 degrees F.) of each other. The conventional or traditional soldering iron systems of PACE(copyright) (the assignee of the present application) which employ RTD""s provide even better absolute temperature accuracy of within +/xe2x88x9215xc2x0 F. or better. The RTD itself (which is laser trimmed and consistent) offers a temperature accuracy within 1%, whereas a K type thermocouple (which is often the reference used for calibrating a soldering iron) may be accurate within +/xe2x88x922.2 degrees Centigrade within a given temperature range (e.g., 0xc2x0 C. to 277xc2x0 C.).
These all would certainly represent acceptable levels of accuracy as well as relatively high degrees of accuracy when compared with existing tip/heater cartridge soldering systems whose true operating tip temperature (as measured at the working end of the tip) can vary by as much as 30xc2x0 F. to 100xc2x0 F. or more from the set, displayed or xe2x80x9cratedxe2x80x9d temperature of the tip.
In traditional soldering stations with removable tips, there are a number of reasons why the true operating tip temperature (as measured at the working end of the tip) varies from the user selected or desired tip temperature. The sensor measuring and controlling the heater output is typically located in the heater itself at some point away from the working end of the tip. Thus, it senses temperature changes at that point and only indirectly senses temperature and thermal load changes affecting the working end of the tip. Depending on the circuit configuration of the temperature control system, the relative masses of the heater and tip, the geometry of the tip and the working load on the tip during use, the true operating temperature of the tip (at idle) can vary as much as 50xc2x0 F. or more from the user selected/displayed temperature on the dial or digital readout. This is particularly evident with large massive tips designed for surface mount component removal. This temperature difference becomes exacerbated when the user selected temperature is increased. It may also be affected when oxides build up between the tip and the heater which inhibits thermal conduction between the two.
Although it is less of an issue for certain types of soldering stations, such as those which use relatively accurate laser trimmed RTD""s (Resistance Thermal Detectors), additional unknown sources of error between the user selected/displayed temperature and the true operating tip temperature are introduced when handpieces or heaters are changed, which occurs, respectively, when workshifts change (each shift operator often has his/her own handpiece) or when the heater burns out. This source of error is due to the wide variation in accuracy between sensors (such as thermocouples) from heater to heater. Furthermore, the temperature accuracy of even a single heater can xe2x80x9cdriftxe2x80x9d over time, thus necessitating periodic calibration even if the handpiece, heater or tip/heater cartridge is not changed.
As suggested above, simply changing the tip in a soldering iron can introduce a significant source of inaccuracy between user selected/displayed temperature and the true operating tip temperature. Unless the system features a tip temperature offset feature which compensates for different tip geometries (such as the assignee""s MBT 250 product) or the user knows how much error a particular tip will create (and can thus, in some way compensate for it), the user selected/displayed temperature and true operating tip temperature can vary greatly.
In the tip/heater cartridge type soldering stations, different tip geometries can also introduce similar errors. In addition, many of these tip/heater cartridges suffer from the same inaccuracies as traditional soldering iron heaters inasmuch as they employ thermocouples or other temperature regulation means which can greatly vary in accuracy from tip/heater cartridge to tip/heater cartridge. Thus, every time a tip/heater cartridge is changed, typically because the tip is worn or the user desires to use a different geometry of tip, a potentially significant unknown temperature error between the set, displayed, or rated temperature of the tip, and the true operating tip temperature is introduced in the soldering station. This is also the case with the Curie point control cartridges. Although tip/heater cartridge stations typically do not allow the user to select and/or display a particular desired tip temperature, the true operating tip temperature can vary greatly, even between two tip cartridges with the same tip geometry and temperature xe2x80x9crangexe2x80x9d or xe2x80x9cratingxe2x80x9d. Furthermore, the temperature accuracy of even a single tip/heater cartridge can xe2x80x9cdriftxe2x80x9d over time thus necessitating periodic calibration even if the cartridge is not changed.
It would be possible to employ more accurate temperature sensing devices, such as a separate RTD sensing circuit in the tip/heater cartridge, but this would be cost prohibitive.
Errors particularly large errors in absolute tip temperature accuracy can lead to serious problems in the electronic manufacturing, rework and repair process including loss of efficiency, poor quality work and damaged work.
To overcome these shortcomings, users or their organizations desire or require periodic calibration to confirm or re-establish performance standards which, among other things, include absolute temperature accuracy.
As mentioned above, even merely changing a heater, handpiece, tip/heater cartridge or a tip can cause an unacceptable error in absolute temperature accuracy thus necessitating calibration of a soldering station or the discontinuance of its use if it cannot be brought into conformance through calibration. Calibration can be accomplished through a variety of means, such as changing the position of a dial/display control relative to the potentiometer shaft or adjusting a separate xe2x80x9ccalxe2x80x9d potentiometer on the power source until the temperature measured by an independent temperature measurement means (of acceptable accuracy) attached to the working end of the installed tip matches the temperature set and/or displayed on the dial or digital readout on the power source. However, in many instances, the calibration procedure is reliable only for the particular set temperature at which it was performed. Once the user changes the set temperature, the desired or required level of absolute temperature accuracy may be lost since the magnitude of the temperature error varies with set temperature.
Soldering station calibration can be quite time consuming, requires the purchase of additional equipment and the training of personnel. It also reduces efficiency and adds cost to the electronic production process as it often necessitates the equipment to be taken out of service or off the production line during the calibration process.
A soldering apparatus processor having temperature selection, calibration and heating control is known from U.S. Pat. No. 5,495,093 (Griffith) has a stored program microcontroller by which one or more temperatures can be selected for a soldering iron tip, and then, the system automatically maintains the tip temperature during the soldering operation. A thermocouple is provided for measuring and calibrating the actual temperature of the iron tip, and an external thermocouple probe is used to separately and simultaneously ensure that the temperature of a probed component does not exceed a predetermined safe level. However, the calibration thermocouple is located on the soldering iron heater element just ahead of the heater end closest to the tip. As a result, tip scaling factors must be utilized to compensate for the temperature offsets at the tip and identification of the type of tip attached to the system.
It is therefore a primary object of the present invention to provide a soldering station with an accurate, quick, easy, low cost, convenient means of self-calibration which can be employed as frequently as desired any time a tip, heater, handpiece or tip/heater cartridge is changed, or routinely such as every time the soldering station is powered on, and which does not require re-calibration when the set or desired temperature is changed after the self-calibration procedure.
It is another primary object of the present invention to provide an economical, self-calibrating tip/heater cartridge soldering station which can provide an improved level of absolute temperature accuracy over those currently in use and known to the industry, even when the set or desired temperature is changed after the self-calibration procedure.
It is yet another primary object of the present invention to provide a self-calibrating soldering station which does not require an independent or separate calibration procedure utilizing other pieces of equipment.
Other features and advantages of the present invention will be apparent from a reading of specification and drawings.
In one preferred embodiment of the present invention, a contact type, calibration temperature sensor of a relatively high accuracy as compared to that of the temperature control system of a tip/heater cartridge is located in the soldering station power source. The contact sensor can be an RTD or other temperature sensing device of acceptable accuracy.
In set-up mode, the user can select whether the self-calibration warning feature is operable. When operable, an LED is illuminated in a red color if the tip/heater cartridge is removed or the handpiece is unplugged while the soldering station is powered on, or simply when the soldering station is powered xe2x80x9conxe2x80x9d from the xe2x80x9coffxe2x80x9d mode. This is intended to alert the user that a self-calibration procedure may be required to ensure compliance of the unit with the desired performance standards.
The user sets the desired tip operating temperature appearing in the LED display using the up/down scroll keys, and with the desired geometry tip/heater cartridge installed in the handpiece, the tip is tinned with solder (to insure good thermal contact with the contact temperature sensor) and is then placed on the contact sensor. The system, through the contact temperature sensor, detects a temperature change and automatically initiates the self-calibration process. After a few seconds, when the temperature detected by the RTD (or other temperature sensing device) stabilizes, it enters into the tip/heater cartridge temperature control system, a temperature offset constant which compensates for any temperature discrepancy between the temperature as measured by the contact temperature sensor and the temperature being controlled by the tip/heater cartridge temperature control system, thus causing the system to achieve a much higher level of absolute temperature control accuracy (comparable to what the RTD would provide if it were in used in the tip/heater cartridge temperature control system). Now, the LED is illuminated in a green color (and/or with some message in the digital display) indicating that the self-calibration operation is completed.
Once the self-calibration process is completed for the installed tip/heater cartridge, the user can alter the desired temperature setting (using up/down scroll keys, a knob, dial, or other setting mechanism) at will without any loss of calibration since an algorithm built into the tip/heater cartridge temperature control system operates on the temperature offset constant causing the temperature compensation to be appropriately adjusted according to the set temperature. This is a non-linear function since the delta between the controlling temperature and the true tip temperature increases as the temperature increases. The use of such algorithms, per se, is known, see the Griffith patent and the PACE(copyright) MBT250 soldering station mentioned above.
In another preferred embodiment of the present invention, this same contact sensor can also be employed in a traditional soldering station of the types described above.